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Chapter 10AgentsAgents represent endpoints where network-layer packets are constructed or consumed, and are used in the implementationof protocols at various layers. The class Agent has an implementation partly in OTcl and partly in C++. The C++implementation is contained in ~ns/agent.cc and ~ns/agent.h, and the OTcl support is in ~ns/tcl/lib/ns-agent.tcl.10.1 Agent stateThe C++ class Agent includes enough internal state to assign various fields to a simulated packet before it is sent. Thisstate includes the following:addr_dst_size_type_fid_prio_flags_defttl_node address of myself (source address in packets)where I am sending packets topacket size in bytes (placed into the common packet header)type of packet (in the common header, see packet.h)the IP flow identifier (formerly class in ns-1)the IP priority fieldpacket flags (similar to ns-1)default IP ttl valueThese variables may be modified by any class derived from Agent, although not all of them may be needed by any particularagent.10.2 Agent methodsThe class Agent supports packet generation and reception. The following member functions are implemented by theC++ Agent class, and are generally not over-ridden by derived classes:Packet* allocpkt()Packet* allocpkt(int)allocate new packet and assign its fieldsallocate new packet with a data payload of n bytes and assign its fields96